Lack of nitrate tolerance in isosorbid dinitrate- and sodium nitroprusside-induced relaxation of rabbit internal anal sphincter

AIM: To investigate the tolerance development against the relaxant effect of nitric oxide donating drug isosorbide dinitrate (ISDN) and sodium nitropruside (SNP) in internal anal sphincter (IAS) smooth muscle. METHODS: Relaxation responses of ISDN, and electrical fi eld stimulation (EFS) were obtained before and after tolerance induction by ISDN incubation. RESULTS: ISDN (10-7-10-4 mol/L) and SNP (10-8-10-4 mol/L) caused a concentration-dependent relaxation on the basal tonus of the isolated rabbit IAS strips. After a period of 2 h incubation of the 6 x 10-4 mol/L ISDN the relaxation effects of ISDN and SNP did not change compared to control strips. EFS evoked frequency-dependent relaxation in internal anal sphincter smooth muscle and Emax obtained from control strips were not changed in ISDN tolerance-inducing condition. In this study nitrate tolerance was not observed in rabbit IAS smooth muscle. CONCLUSION: This result shows that nitric oxide donating drugs relaxes the internal anal sphincter of the rabbits without the development of tolerance.

Internal anal sphincter augmentation and substitution

There is an increasing recognition of the importance of internal anal sphincter(IAS)dysfunction presenting as passive faecal incontinence.This problem may manifest after anal sphincterotomy or following the more minimally invasive operations for haemorrhoids,as well as with advancing age.Because of the poor results of IAS plication and the beneficial outcomes with peri-urethral bulking agents in urology,these materials have been developed for use in IAS dysfunction.This review outlines the basic purported mechanisms of action,defining the materials in clinical use,their methods of deployment,complications and reported outcomes.There is still much that is unknown concerning the ideal agent or the volume and the technique of deployment,which will only be answered by powerful,prospective,randomized,controlled trials.The specific role of autologous stem cells designed to regenerate the sphincters in cases of functional impairment or muscle loss is yet to be seen.

RELATIONSHIP BETWEEN INTERNAL ANAL SPHINCTER FUNCTION AND LENGTH OF REMAINING RECTUM AFTER RESECTING RECTAL CARCINOMA

Objective: To study the relationship between internal anal sphincter function and length of remaining rectum after resecting rectal carcinoma. Methods: Preoperatively, 21 patients were evaluated via patients' clinical date, including anal resting pressure (resting pressure) assay. Six months postoperatively, repeated manometric studies and clinical evaluations were performed to assess the level of continence . The formula use for calculating post operative resting pressure is as follows: postoperative resting pressure=0.42×preoperative resting pressure+1.56×length of remaining recturm+12.37(R 2=0.58; P <0.01).Degree of continence was graded based on severity of the dysfunction and grade of the continence score. Results: It was demonstrated the patients with low postoperative resting pressures (<4.0 Kpa) had incontinence, and those with high postoperative resting pressures (>4.7 Kpa) were continent. There were significant correlations between length of the remaining rectum and ratio of the decrease in maximum resting pressure (postoperative/preoperative maximum resting pressure;r=0.62; P <0.01). Conclusion: Continence of rectum is influenced by maximum resting pressure of function of the internal anal sphincter, length of remaining rectum is shorter, the more damage to the internal anal sphincter. It is able to foretell stool incontinence by using the postoperative resting pressure formula, and to determine the length of the remaining rectum.

Role of three-dimensional endoanal ultrasound in assessing the anal sphincter morphology of female patients with chronic proctalgia

AIM To assess the role of three-dimensional endoanal ultrasound (3D-EAUS) for morphological assessment of the anal sphincter of female patients with chronic proctalgia (CP). METHODS In this unmatched case control study, 30 consecutive female patients with CP and 25 normal women (control group) were enrolled. 3D-EAUS was performed in all subjects. Thickness and length of internal anal sphincter (IAS), thickness of puborectalis muscle (PR), length of the external anal sphincter (EAS) plus PR, and puborectalis angle were measured and compared between the two groups. RESULTS Patients with CP had significantly shorter IAS length and greater PR thickness, as compared to those in normal individuals (26.28 +/- 3.59 mm vs 28.87 +/- 4.84 mm, P < 0.05 and 9.67 +/- 1.57 mm vs 8.85 +/- 0.97 mm, P < 0.05, respectively). No significant between-group differences were observed with respect to IAS thickness and the EAS plus PR length (P > 0.05). Puborectalis angle in the CP group was significantly decreased, both in resting (88.23 degrees +/- 1.81 degrees vs 89.94 degrees +/- 2.07 degrees in control group, P < 0.05) and straining (88.47 degrees +/- 3.32 degrees vs 90.72 degrees +/- 1.87 degrees in control group, P < 0.05) phases, which suggest the presence of paradoxical contraction of PR in patients with CP. In the CP group, no significant difference in puborectalis angle was observed between the resting and straining phases (88.23 degrees +/- 1.81 degrees vs 88.47 degrees +/- 3.32 degrees respectively, P > 0.05). CONCLUSION The association of greater PR thickness and paradoxical contraction of PR with CP suggest their potential value as markers of CP.

Endoanal ultrasonography in fecal incontinence: Current and future perspectives

Fecal incontinence has a profound impact in a patient's life, impairing quality of life and carrying a substantial economic burden due to health costs. It is an underdiagnosed condition because many affected patients are reluctant to report it and also clinicians are usually not alert to it. Patient evaluation with a detailed clinical history and examination is very important to indicate the type of injury that is present. Endoanal ultrasonography is currently the gold standard for sphincter evaluation in fecal incontinence and is a simple, well-tolerated and non-expensive technique. Most studies revealed 100%sensitivity in identifying sphincter defect. It is better than endoanal magnetic resonance imaging for internal anal sphincter defects, equivalent for the diagnosis of external anal sphincter defects, but with a lower capacity for assessment of atrophy of this sphincter.The most common cause of fecal incontinence is anal sphincter injury related to obstetric trauma. Only a small percentage of women are diagnosed with sphincter tears immediately after vaginal delivery, but endoanal ultrasonography shows that one third of these women have occult sphincter defects. Furthermore, in patients submitted to primary repair of these tears, ultrasound revealed a high frequency of persistent sphincter defects after surgery. Three-dimensional endoanal ultrasonography is currently largely used and accepted for sphincter evaluation in fecal incontinence, improving diagnostic accuracy and our knowledge of physiologic and pathological sphincters alterations. Conversely,there is currently no evidence to support the use of elastography in fecal incontinence evaluation.